I have to design a circuit that simulates a voltage spike on a dc supply rail. The circuit has a button that, when pressed, generates a short pulse of controllable height (controlled by pot). The internal circuitry essentially has to sit a pulse train on top of a constant dc voltage.
The voltage values are somewhat strict; they are shown in the diagram. The pulse height is controlled anywhere from 0v to 4v and the dc offset is 5.28v. From the diagram, you can see that the output from the 555 and the dc offset voltage are buffered for isolation.
My problem is that with a single rail power supply, the op amps cannot do the summing because the output will be inverted.